This invention relates to electric actuators and more particularly to high torque-to-weight ratio electric actuators for use in robotic systems.
As is well known in the art, robotic systems can be used to reduce or eliminate manual operations in certain industrial operations. This reduction in manual operations may often result in significant productivity improvements in the operation. Moreover, in hazardous or limited access environments the use of robotic systems may not only be advantageous but may also be a necessity. For example, in the repair or maintenance of nuclear reactor power plants, it is important to be able to limit the time that working personnel are located in a radioactive environment so as to limit the working personnel's radiation exposure. Thus, the use of robotic systems in nuclear power plant maintenance can result in both improved productivity and in decreased radiation exposure.
In robotic arm systems, the elements which power the movements of the robotic arm may be located away from the arm joints (driving the joints by means of chains or belts) or the elements may be located at each joint. The use of actuators located at each joint decreases the compliance of the arm, but reduces the arm's load capability due to the added weight of the actuator on the arm. On the other hand, the use of actuators located remote from the joint reduces the weight of the arm, but increases compliance and accuracy of the arm's movement. It is therefore desirable that actuators located in the arms be both powerful and lightweight. Traditionally, such actuators have been hydraulic-type actuators because no electric actuator could match the torque-to-weight ratios of hydraulic actuators. Hydraulic systems, however, are more difficult to control, are not capable of continuous rotation (vane type), and require a large amoung of peripheral equipment (i.e. pumps and accumulators). Also, when used in environments where human access is limited, the possibility of contamination by the hydraulic fluid exists.
Therefore, what is needed is an electric actuator having a high torque-to-weight ratio and capable of being mounted in an arm of a robotic system.